This invention relates to the preparation of stable formulations of manganese (II) ethylenebis-(dithiocarbamate) (maneb) and, more particularly, to the preparation of aqueous formulations of maneb having unexpectedly low concentrations of ethylenethiourea (ETU).
Maneb is a known important fungicide, but the compound is unstable and tends to decompose. Decomposition products, such as ethylenethiourea (ETU), appear in freshly made maneb and increase in concentration during periods of storage.
Although much work has been done which relates to improving the stability of maneb, there are no known references which teach the present invention.
L. Donev [Khimiyai industriya (Sofia) 41, 100-101 (1969), No. 3], for example, teaches a method of preparing maneb of increased dithiocarbamate content in which aqueous formaldehyde is added to a manganese(II) sulfate solution. Then a solution of ammonium ethylenebis(dithiocarbamate) (amobam) is added to precipitate the maneb. ETU concentration is not discussed.
U.S. Pat. No. 3,856,836 discloses a maneb derived from a formaldehyde-treated reaction mixture. The maneb is precipitated in aqueous medium from a water-soluble salt of ethylenebis(dithiocarbamic acid) and a water-soluble manganese(II) salt. Formaldehyde is added to the reaction mixture after precipitation. The reference does not discuss ETU concentration.
U.S. Pat. No. 2,974,156 teaches that hexamethylenetetramine (HMTA) can be added to maneb to improve stability.
U.S. Pat. No. 3,173,832 teaches that paraformaldehyde can be added to maneb to improve stability and that a soluble zinc salt can reduce phytotoxicity.
Although the prior art discloses various methods of formulating maneb to improve strength and/or stability of the product, no known references discuss the preparation of maneb having a low ETU concentration, either as a dry or an aqueous product.